Double hung windows feature a balancing arrangement to counter the weight of the window sashes, thereby permitting a user to position the sashes at a desired opened height. The balancing arrangement also enables the user to open and close the windows with minimum exertion.
Traditionally the aforenoted counter balancing has been accomplished via a pulley, weight and rope arrangement. In modern double hung windows the pulley, weight and rope arrangement has been replaced by a spring arrangement of one type or another. A "constant force" spring arrangement is commonly used.
An important feature of modern double hung windows is the weather stripping which seals against seepage of hot and cold air. One of the prime locations for a weather stripping seal is the horizontal center of the window, i.e. where the bottom of the top and the top of the bottom window sashes meet.
Most weather stripping seals are of a flexible material and the compression of the material provides the seal. It has been found that compression of the weather stripping material can require a force greater than the balancing force needed for raising and lowering the window sashes. Accordingly, when the bottom sash is raised to a venting position and the user desires to lower the sash to close the window, the force required for compressing the weather stripping at the meeting rail, i.e. the horizontal center of the window, displaces the top sash downward, causing a poor seal and also causing poor alignment of the sash locks.
The invention herein disclosed overcomes this problem by incorporating a leaf spring and detent into the window balancing arrangement associated with at least the top sash, whereby the aforenoted displacement of the sash is prevented and the effectivity of the weather stripping seal is maintained.